The present invention relates to the field of building materials, and more particularly to acoustical panels for walls, ceilings, movable partitions and other interior surfaces in commercial and residential construction. These are porous materials designed for acoustic absorbency.
Acoustical panels for walls and ceilings provide sound absorption, aesthetics, and separate utility space in ceilings. Manufacturers strive to develop decorative acoustical ceiling panels at the lowest possible cost by continuously refining the manufacturing process in an effort to reduce energy use, materials costs and waste. While cost reduction is important, there is an inherent limit to how much the process can be simplified and still produce a panel that meets the requirements of acoustical performance, moisture resistance, and fire resistance.
Typical wallboard manufacturing begins with gypsum that is mined and crushed as gypsum rock or obtained synthetically from flu gas desulfurization plants. In the calcination process, the powdered gypsum is heated to dehydrate the gypsum to a hemihydrate. The calcined gypsum or hemihydrate is known as stucco. Fillers such as perlite and fiberglass are added to the stucco to achieve the desired properties of the finished wallboard. Other additives include starch to help adhere the core to the paper face. Retarders and accelerators may be added to adjust the reaction rate. These ingredients are combined with water and soap foam in a high speed or pin mixer. Although soap foam is added to lower the core density, the resulting structure may not have sufficient porosity to be considered acoustic. The resulting mixture is placed between two sheets of paper and sized for thickness by a roller. After the core sets up, the board is cut to length then transferred to an oven to dry.
Current methods of producing acoustical ceiling panels utilize various combinations of fibers, fillers, binders, water and surfactants mixed into a slurry which is processed into panels. This process is very similar to the methods used in papermaking. Examples of fibers used may include mineral fiber, fiberglass, and cellulosic material. Mineral wool is a lightweight, vitreous, silica-based material spun into a fibrous structure similar to fiberglass and may also be used. Mineral wool enhances acoustical performance, fire resistance, and sag resistance of an acoustic panel.
Fillers may include expanded perlite and clay. Expanded perlite reduces material density and clay enhances fire resistance of the acoustical panel. Examples of binders used in acoustical panels may include starch, latex and/or reconstituted paper products, which link together and create a binding system that locks all of the ingredients into a structural matrix.
The above ingredients, when combined and processed appropriately, produce a porous, sound absorbent panel suitable for use as acoustic ceiling panels and other types of construction panels. Today, such panels are manufactured using a high volume process that resembles paper production.
Traditional fabrication methods of forming panels incorporating a mineral wool fiber, perlite filler and cellulosic binders, rely upon aggregation and flocculation of the cellulosic ingredients. The resulting aqueous cellular foam is dried to provide a stable structure within which fiber, binders and fillers flocculate and bond to create a matrix. While an aqueous cellular foam mixture may include a surfactant to facilitate the entrainment of air into the mixture the traditional methods of fabrication rely upon flocculation. The structure of a typical ceiling panel material is shown in the 30xc3x97photomicrograph of FIG. 1. The perlite particles are discernable as round nodules embedded in an interconnecting matrix of mineral wool and reconstituted newsprint fibers.
Current processes for manufacturing ceiling panels are complex, include many steps, and use large amounts of water and energy. During the process, water is progressively removed from the product through a combination of draining, pressing, and high-temperature oven heating. Some drained water may be recycled, but a majority is treated and released into the environment.
Different production processes and slurry recipes yield panels with differing acoustical and structural characteristics. There is a tradeoff between the acoustical performance and the durability. A highly porous, low-density material may exhibit the best acoustical performance. Unfortunately, a low-density material tends to be fragile and difficult to handle and exhibits low durability, low scrubability, and low tensile strength. For the purpose of this disclosure, the term durability refers to a panel""s compressive yield strength which is a measure of how easily panel material deforms under compression. Resistance to finger indentation is an example of good compressive yield strength. Scrubability is the resistance to abrasion by repeated back and forth motion of a wet scrub brush. Tensile strength refers to the ability to lift or support a panel along one edge without the panel breaking.
Various processes and recipes are used to balance the tradeoffs inherent in the manufacture of acoustical ceiling panels. For example, one common structure for a ceiling panel is a laminate, using different layers of material, as shown in FIG. 2. One layer 201 comprises a soft, acoustically absorbent material, while the other layer 202, which faces into the room, is a more durable, sometimes structural material that is relatively transparent to sound. The acoustical performance of the panel is largely a function of the inner layer 201, while the outer layer 202 enhances the durability, scrubability, and aesthetics. The outer layer 202 in FIG. 2 may be a third-party supplied material. Normally, an adhesive attaches the overlay 202 to the inner layer 201. Other steps involved in the manufacture of laminated panels include painting, cutting to size, and packaging.
Laminated panels provide a good balance between performance and durability. Such panels have the advantage of being susceptible to continuous manufacturing processing in certain steps, but require additional process steps and additional materials, e.g. the outer layer material and adhesive, which are not required when producing a homogeneous panel. Furthermore, the outer layer material usually is a high-cost constituent and the lamination process requires additional machinery, materials, and human resources. While the production of the acoustical material 201 component can typically be done in continuous fashion, the lamination step is not a continuous process. As a result, laminated panels are relatively expensive to manufacture.
Casting or molding processes are also used to create a panel structure as in FIG. 1. Casting produces a homogeneous material that is very durable and has good acoustical properties. Cast materials generally have a much higher density, and do not require the additional layer present in laminated construction. Casting is essentially a batch process in which the material is poured into a mold. The bottom of the mold is typically lined with a carrier or release agent to prevent sticking. The materials are dried in the mold, the mold is removed, and the panel undergoes a finishing process. Molded panels usually have good mechanical strength properties and exhibit good durability but the acoustical performance is generally not as good as a laminated panel. Drawbacks to the molding process include: the requirement of moving molds continuously throughout the process, smaller panels resulting from mold size constraints; the requirement of the added step of panel removal from the molds; and higher material cost per panel because of increased panel density.
Another common method of producing a panel having the structure shown in FIG. 1 is to extrude the slurry onto a wire belt, and allow the water to drain from the slurry. Other process steps include forming, drying, and surfacing or sanding resulting panels to create the desired texture in a nearly continuous process to produce an acoustically absorbent layer. Process steps such as embossing or punching small holes into the material may further enhance the acoustical absorbency of the panel. Disadvantages include higher energy costs for drying and the treating of discharge water.
With the foregoing problems in mind, there is a need to produce a low-density material for use in ceiling and other structural panels having good acoustical performance, while maintaining structural durability of the material.
Additionally, there is a need to produce a panel with high sag resistance, improved durability, a high Noise Reduction Coefficient (NRC) and a high Sound Transmission Coefficient (STC).
A common method of producing a panel having high STC is to apply a backing material such as foil or an organic coating to the backside of the acoustic panel. The application of backing materials adds additional processing steps and cost to the finished product.
Furthermore there is a need to create a panel that does not require additional additives to enhance fire resistance and to create a non-homogeneous panel with a hard, high-density surface on at least one side.
The acoustically absorbent porous panels of the present invention are comprised of a cured aqueous foamed cementitious material wherein the resulting panel is comprised of at least 90% by weight of cementitious material. Additionally, the aqueous foamed cementitious material is comprised on a wet basis of about 53% to about 68% by weight cement, about 17% to about 48% by weight water, about 0.05% to about 5% weight fiber, and about 0.01% to about 10% weight surfactant. The panel further includes pores distributed within the cured material comprising about 75% to about 95% by volume of the panel.
Additionally, the present invention includes an acoustically absorbent porous panel where the resulting panel is comprised of at least 90% by weight of the cementitious material. The foamed cementitious material is comprised on a wet basis about 54% to about 63% by weight cement, about 32% to about 44% by weight water, about 0.1% to about 3% by weight fiber, and about 0.5% to about 5% by weight surfactant with pores distributed within the cured material comprising about 75% to about 95% by volume of the material.
The present invention includes an acoustically absorbent porous panel where the resulting panel is comprised of about 95% by weight of the cementitious material. The foamed cementitious material is comprised on a wet basis about 56% to about 61% by weight cement, about 32% to about 42% by weight water, about 0.28% to about 1.3% by weight fiber, and about 0.7% to about 2% by weight surfactant with pores distributed within the cured material comprising about 75% to about 95% by volume of the material.
Furthermore, the present invention includes a process for producing the acoustically absorbent porous panel. Within the process a foam slurry comprising between about 53% to about 68% by weight cement, between about 17% to about 48% by weight water, between about 1% to about 10% by weight calcium silicate, between about 0.05% to about 5% by weight synthetic organic fibers and between about 0.01% to about 10% by weight surfactant is aerated or whipped to include air within the slurry. The aerated foamed slurry is then dried to a moisture content of less than about 5% by weight water.
The present invention can also be characterized as an acoustically absorbent porous panel formed from cementitious material, fibers and surfactant. Wherein the formed panel has a density between about 10 and 40 lb/ft3 and an indent of less than 0.12 inches. The formed panel also has a Noise Reduction Coefficient of at least 0.5, an STC between and including 30 and 40, and a sag test result of less than 0.150 inches at 90% RH.
These and other features of the present invention will become more apparent upon review of the following description, when taken in conjunction with the accompanying drawings.